You can mold Kydex on one of Ring's blue guns. Note that Blue Guns need work "blocking" a number of areas to build the holster properly. But to your original question, Kydex doesn't require that much heat that the replica would be damaged.

Blue guns can be used as Kydex cools quickly enough and is not heated enough to distort the Blue Gun. If it is you will ruin the Kydex...As mentioned blocks are needed to mold the holster correctly, along the sight channel and where anything like a paddle or strap may be bolted on that the screws would contact the firearm

If you feel it is necessary to buy a mold gun/ drone go to multimolds.com. Nobody uses blue guns in the "Dex" holster making world, they are inferior to the aluminum/ poly mixtures being used.Blocking and sight channel's are all done as multi molds designs their mold guns for holster makers. Plan on spensding 60-70 bucks on a mold gun. TIP: try my buddies at Omegaholsters.com (owner Nate) in lieu of buying a mold gun. He stocks over 80 models! He is a LEO in Texas and a good man. Hope this helps you.

I too prefer Multi-Molds. I also still do quite a bit of blocking on the multi-mold before molding Kydex.

I use several other brands, I had an issue with a bunch of P239 holsters I built for members here, and found the mold was undersized. You should never expect a mold to be perfect, they are cheaply produced and not exact.